JPS6048112B2 - Electrical/mechanical conversion element - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides an electric
It relates to a mechanical transducer, such as a bimorph.

Recently, efforts have been made to make the recording track width as narrow as possible in magnetic recording and reproducing devices (VTRs) in order to increase the recording density as much as possible. Accordingly, higher accuracy is required in the positional relationship of the reproducing magnetic head with respect to the recording track.

Since it would be technically difficult to simply make this positional relationship depend on the mechanical precision of the device or would result in a considerable increase in cost, an electro-mechanical transducer was used, and thereby the magnetic A method is adopted in which the positional relationship of the head with respect to the recording track is always controlled to a predetermined relationship. Immediately
The magnetic head is mechanically connected to an electromechanical transducer element, and the magnetic head constantly records an electric signal caused by a change in the reproduction signal caused by a change in the positional relationship between the magnetic head and the recording track. Set it so that it is in the correct position relative to the track. Normally, the bimorph element used in the tracking servo of such a VTR needs to be able to obtain a large displacement with a low voltage.

In particular, for VTRs with wide track widths, there are several hundred to six
A large displacement of about 00 μm is required. As shown in FIG. 1, a normal bimorph element has two piezoelectric plates 2 each having an electrode 1 adhered to each main surface, and is called a shim plate interposed between these piezoelectric plates 2. They are laminated and bonded to plate-like members 4 with adhesive 3, respectively.

The piezoelectric plate 2 is made of a piezoelectric material such as ceramic, polymer, or a composite material of ceramic and polymer, and the shim plate 4
, titanium, stainless steel, phosphor bronze, etc., and as the adhesive 3, a conductive adhesive is used. In this configuration, when voltage is applied between the opposing electrodes 1 to both piezoelectric plates 2 so as to apply electric fields in opposite directions, one piezoelectric plate 2 expands and the other contracts, causing displacement. occurs. That is, as shown in FIG. 1, when one end of the bimorph is mechanically fixed, that is, clamped, the other end is displaced as shown by the arrow. However, with such a normal bimorph, it is not possible to obtain as large a displacement as shown on the left.

Now, as shown in FIG. 2, if a required voltage is applied between the electrodes 1 on both main surfaces of the piezoelectric plate 2, which has electrodes 1 adhered to both main surfaces, the piezoelectric plate 2 It expands and contracts depending on the direction of the electric field, but since this expansion and contraction occurs in the directions x and y that are orthogonal to each other, one surface of the piezoelectric plate 2 has a shim plate made of a metal plate as described above. When it is mechanically fixed, that is, clamped, in both the x and y directions by a reinforcing plate 4 whose elastic modulus is the same in the x and y directions, that is, is isotropic, as shown in FIG. 3, This will result in 1 sore in both the x and y directions.

Therefore, if only displacement due to warpage in one direction, for example the x direction, is required, the warpage that occurs in the y direction will rather structurally inhibit the occurrence of warp in the x direction. Furthermore, in the structure illustrated in FIG. 1, a polymeric adhesive is generally used as the adhesive 3, but the flexibility of this adhesive inhibits the ramping of the piezoelectric plate 2 to a certain degree, as described above. The occurrence of warping is suppressed.

In the present invention, as mentioned above, isotropic expansion and contraction,
Based on the investigation that it is not possible to obtain sufficient displacement in the above-mentioned electromechanical transducer due to the influence of adhesive,
This makes it possible to obtain a large displacement in an electromechanical transducer such as a bimorph or a monomorph.

That is, in the present invention, a first member is made of a piezoelectric plate having electrodes adhered to at least both main surfaces, and a plate-shaped second member is, for example, three shim plates that provide a reinforcing or clamping effect. In the present invention, the second member is composed of a member having anisotropic elastic modulus, and the two members are orthogonal to each other. Regarding the first and second two directions x and y, the elastic moduli Ex and Ey have the relationship Ex>Ey, and the elastic modulus E of the piezoelectric plate of the first member is the same as that of the second member. The elastic modulus is greater than the smaller elastic modulus, that is, the relationship E>E is established. Next, the electro-mechanical conversion element according to the present invention will be explained in detail.

An example of applying the present invention to a bimorph will be described with reference to FIGS. 4 and 5.

In this example, two piezoelectric plates, ie, a first member 12, each having an electrode 11 adhered to its main surface, are provided and are laminated together with a second member 13 interposed between them.

The first member 12, that is, the piezoelectric plate, is composed of a piezoelectric ceramic plate made of, for example, lead zirconium titanate.

The second member 13, that is, the shim plate interposed between the piezoelectric plates and having a clamping or reinforcing effect, is made of a material particularly having anisotropy in elastic modulus.

This member 13 may be, for example, a carbon fiber sheet in which a carbon fiber layer extending in one direction is impregnated with, for example, epoxy adhesive. This carbon fiber sheet exhibits a maximum elastic modulus in the direction in which the carbon fibers extend, and a minimum elastic modulus in a direction perpendicular to this direction.
When constructing a bimorph with this carbon fiber sheet, the direction in which expansion and contraction is required to contribute to obtaining the displacement, in the illustrated example, the X direction, is the direction in which the maximum elastic modulus is exhibited, , arranged so that the carbon fibers extend in the same direction. Further, embodiments of the bimorph according to the present invention will be described in detail.

Example 1 The first member 12, that is, the piezoelectric plate, has a thickness of 250 mm.
A piezoelectric plate 2 made of μm lead zirconium titanate (PZT)-based piezoelectric ceramic is prepared, and both main surfaces thereof are coated with, for example, Au.
An electrode 11 is formed by vapor depositing.

On the other hand, a carbon fiber sheet with a thickness of 100 μm is prepared by arranging carbon fibers 15 with a diameter of 10 μm so as to extend substantially in one direction and impregnating this with an epoxy adhesive 16. As,
It is sandwiched between the two piezoelectric plates 12 described above. In this state 1
The adhesive is cured by heat-pressing at 20 DEG C. to 130 DEG C. for 3 hours to produce a bimorph of 25 mm x 25 rfrIn. The direction of fiber extension of the shim plate 13 of this bimorph is x
The direction perpendicular to this and along the plate surface direction of the bimorph is defined as the y direction, one end in the
0772117! Curve 14 in FIG. 6 shows the results of measuring the displacement in the direction perpendicular to the plate surface direction of the bimorph at each position in the range of 20Tf0fL. In addition, one end in the y direction is similarly fixed over a width of 5wn, and from the center of the free end in the x direction, each side is 10770F.
! Curve 15 in FIG. 6 shows the results of measuring the displacement in the direction perpendicular to the plate surface direction of the bimorph at each position within a range of 20 mIn. These curves 14 and 15
As is clear from comparing the following, the displacement position (hereinafter referred to as displacement position in the X direction) when one end in the x direction along the extension direction of the carbon fiber is fixed is:
Compared to the displacement when one end in the y direction is fixed (hereinafter referred to as displacement in the y direction), the displacement is approximately 25 times greater at the center position and approximately 1.8 times greater at both end positions, that is, exhibits high sensitivity. The reason why the displacement in the y direction is lower than that in the , or when expansion and contraction occurs due to the electrostrictive effect, in this y direction, the shim plate 13 expands and contracts to some extent as the piezoelectric plate 12 expands and contracts, and the clamping effect becomes smaller. It is thought that warpage is less likely to occur in the piezoelectric plate 12 and large displacements cannot be obtained. In contrast, in the X direction, this direction is along the longitudinal direction of the carbon fibers of the shim plate 13 and its elastic modulus is large, so the clamping effect on the piezoelectric plate 12 is large, and therefore a large displacement occurs. In addition, by suppressing the occurrence of warpage in the y direction described above, warpage in the X direction is more likely to occur, and a larger displacement can be obtained. and,
Comparing curve 14 with curve 15, the drop in displacement at the center is smaller than that of curve 14 and curve 15. This is because the occurrence of warpage in the x and y directions is likely to be suppressed by the warpage in the other directions, especially in the respective centers, but as mentioned above, in this bimorph, the warpage in the y direction is Since this is less likely to occur, a large amount of warpage in the X direction can be obtained even in the center, and it is thought that a decrease in displacement in the center can be avoided. In addition, as in the above-mentioned example, a bimorph obtained by impregnating a fiber such as carbon fiber with adhesive as the shim plate 13, interposing it between the piezoelectric plates 12, and performing compression hardening is shown in FIG. As shown in the enlarged sectional view of the main part, the fibers 15 are bonded with an adhesive 16, but in this case, the fibers 15 are almost directly in contact with the piezoelectric plate 12 having the electrodes 11 and bonded. Therefore, the adhesive 16, which is relatively flexible and easily slips, is hardly interposed or only very thinly interposed between the two, so that the clamping effect of the adhesive 16 is inhibited. You can avoid being exposed.

Note that the terminals are led out from the electrodes 11 on each inner side of the first member, that is, the piezoelectric body plate 12, from the second member, that is, the end of the shim plate 13 on the fixed side of the bimorph, so as to be in contact with these electrodes 11. A conductive layer 20 such as a metal foil or a vapor-deposited metal layer may be applied to the conductive layer 20, and the terminals may be led out from the conductive layer 20.Alternatively, a cutout may be provided in a part of the shim plate 13 (not shown) and the above-mentioned method may be used. A part of the inner electrode is exposed and the terminal is led out.

Next, in order to clarify the characteristics of the present invention, a comparative example according to the present invention will be described.

Comparative Example 1 In the bimorph described in Example 1, a so-called polymer piezoelectric plate made of a composite material of polyvinylidene fluoride and piezoelectric ceramic powder was used as the piezoelectric plate 12 instead of the piezoelectric ceramic.

The displacement position of the bimorph according to this comparative example was measured by the same measuring method as the displacement measurement method for the bimorph according to Example 1 described above, and the displacement position in the X direction and the displacement position in the y direction were measured. , as shown by curves 17 and 18 in FIG. 8, respectively. As is clear from these curves 17 and 18, there is almost no difference between the displacement position in the x direction and the displacement position in the y direction. In other words, although this comparative example uses a shim plate with an anisotropic elastic modulus and a larger elastic modulus in the X direction than in the y direction, there are no changes in the There is no difference in position. This is because the piezoelectric plate in the bimorph according to this comparative example is made of a polymeric piezoelectric plate θ, and its elastic modulus is even smaller than the elastic modulus in the y direction, which indicates the small value of the elastic modulus of the shim plate. This seems to be because the effect is too strong. Here, in the present invention, the piezoelectric plate 12
The elastic modulus E of (first member) is y of the shim plate (second member)
There is a reason why the elastic moduli of the first and second members are selected so as to maintain a relationship in which the elastic modulus E in the direction is larger. Incidentally, the elastic modulus of the piezoelectric ceramic in Example 1 is 5 to 10×
1 (1f'KgIcILlFor example, in 7x1IK9nod, the fiber direction of the carbon fiber sheet is 13.5x
1Cf'KgIcItl In the direction perpendicular to this, it is 1
．． 0×1Cf'K9k! t, that of the polymer piezoelectric material in Comparative Example 1 is 2.6×101k91d.

Further, Tl of the conventional shim plate is 10X1σKgI (:7i. In the first embodiment, as the shim plate 13, x
Although the arrangement is such that the fibers of the shim plate 13 have the maximum elastic modulus in the direction and the minimum elastic modulus in the y direction, the fiber extension direction of the shim plate 13 does not coincide with the x direction and maintains a certain angle. It is also possible to do so.

Now, in Example 1, the displacement position of each bimorph in the X direction was measured by changing the angle θ between the extension direction of the carbon fibers of the shim plate 13 and the X direction in increments of 00 to 5. The results shown in curve 17 were obtained. 9th
The displacement indicated by the broken line a in the figure is the value when a metal plate is used as the shim plate of the bimorph as in the conventional case, and this value almost corresponds to the case where the angle θ is 45 genus. That is,
When the angle θ is selected to be 45 or less, anisotropy in the elastic modulus of the shim plate occurs, which has the effect of increasing sensitivity. Incidentally, Table 1 shows the fiber direction and X of the carbon fiber sheet as the shim plate 13 explained in Example 1.
The measurement results of the elastic modulus Ex in the x direction and the ratio of this to the elastic modulus Ey in the y direction are shown when the angle θ with the direction is changed. Further, as described above, when using a sheet with fiber arrangement such as carbon fiber as the second member 13 having anisotropy in elastic modulus, the extension and departure of the fibers t
The arrangement is not limited to the case where the dimensions are arranged in one direction with the dimensions 1 and 2 and 3. A sheet in which fibers 15 such as carbon fibers are arranged at an angle of 10 θ, and a sheet in which fibers 15 such as carbon fibers are arranged at an angle of 1 θ in the y direction as similarly shown by 7 thin lines. They can be laminated or integrated, or in some cases, similar fibers (not shown) may be arranged between both sheets in the θ=90 direction for reinforcement in the y direction. It is also possible to laminate them together with a sheet interposed therebetween, or to construct them as a whole in a harmonious manner. As mentioned above, according to the configuration of the present invention, it is possible to obtain a large displacement, so as mentioned at the beginning, for example, VTR
It is suitable for use in tracking servo of a magnetic head, and enables low voltage driving for the same displacement position.

In addition, as in the above example, when a sheet made of fibers such as carbon fiber impregnated with adhesive is used as the second member, that is, the shim plate, the conventional process of applying adhesive is unnecessary. Therefore, the manufacturing process can be simplified,
In turn, it is possible to reduce the price. Further, since the displacement in the y-direction, which does not contribute to obtaining a displaced position, is suppressed, it is possible to avoid the occurrence of cracks during large amplitude operation. In the above example, the present invention was mainly applied to a bimorph formed by laminating two piezoelectric plates, but the present invention can also be applied to electromechanical transducers having various configurations including the bimorph. It is obvious that it can be applied.

[Brief explanation of the drawing]

FIG. 1 is an enlarged sectional view of a conventional bimorph, FIGS. 2 and 3 are explanatory diagrams thereof, FIG. 4 is an enlarged sectional view of an example of the electromechanical conversion element according to the present invention, and FIG. 5 is its essential part. FIG. 6 is a diagram showing the measurement results of the displacement, FIG. 7 is an enlarged cross-sectional view of the main part of the device of the present invention, and FIG. 8 is a comparative example for the present invention. FIG. 9 is a diagram showing the measurement results of the relationship between the direction of the fibers and the displacement position of the second member used for explaining the present invention, and FIG. It is an enlarged plan view of the second material of the example. 12 is a piezoelectric plate, that is, a first member; 11 is an electrode thereof; and 13 is a shim plate or a reinforcing plate, that is, a second member.

Claims (1)

[Claims] 1. Consists of a first member made of a piezoelectric plate with electrodes adhered to both main surfaces, and a second member fixed to one main surface of the first member, the second member comprising: the elastic modulus in a first direction is greater than the elastic modulus in a second direction orthogonal to the first direction,
and an electromechanical conversion element in which the elastic modulus of the first member is selected to be larger than the elastic modulus of the second member in the second direction.